Type 2 diabetes disproportionately burdens African Americans, and already excessive rates of diabetes are expected to increase even further as rates of obesity rise. While there is evidence that diabetes self-management training is effective in improving metabolic control, and modest weight loss can delay the onset of diabetes, we have limited knowledge of the best approach to self-management training from a family perspective in high risk groups such as African Americans. Family remains a valued dimension of African American life and may be an important behavioral context for interventions to improve disease management and health outcomes. Nonetheless, there are no trials of family-based interventions to improve diabetes self-care and achieve weight loss that have involved adult families. The primary aim of the proposed research is to conduct a randomized controlled trial to test the effectiveness of a culturally specific family-based diabetes self-management intervention in overweight/obese African American adults with type 2 diabetes (the "index participant") enrolled with an overweight family member (co-participant). The primary outcome is weight change in the index participant. Given the very early stage of family-based intervention research for adults with type 2 diabetes, and the importance of testing a culturally specific intervention, this project includes 2 formative aims that precede and inform the family-based intervention. The formative aims include a validation study (n=200) to assess the construct validity and reliability of family interaction surveys among African Americans with diabetes. In addition, qualitative data from focus groups (n=4) with both patients with diabetes and family members will be used to refine the intervention. The randomized controlled trial will test the effectiveness of a 6-month family-based diabetes self-management intervention, compared to usual care, among 80 overweight/obese African American adults (index participants) and their family member co-participants. The family-based intervention consists of 20 weekly group sessions. The primary outcome is weight change in the index participant, and secondary outcomes include change in hemoglobin A1c in the index participants, weight change in the co-participants, and change in blood pressure, diet, physical activity, and psychosocial factors in both the index- and co-participants. This culturally specific, family-based diabetes intervention for adult African Americans has the potential to improve diabetes care and reduce complications, and thus has important clinical and public health implications for African American families.